1. Field of the Invention
The present invention relates to a sheet of ultraviolet-cutoff glass capable of cutting off or blocking ultraviolet rays applied thereto and also of repelling water applied thereto, and a sheet of heat-cutoff glass capable of cutting off or blocking heat radiations applied thereto and also of repelling water applied thereto.
2. Description of the Related Art
Some window glass sheets for use on automobiles comprise sheets of ultraviolet-cutoff glass capable of cutting off or blocking ultraviolet rays applied thereto in order to protect automobile drives and passengers from being sunburned and also protect seats and other interior parts from being deteriorated by ultraviolet radiations. Conventional sheets of ultraviolet-cutoff glass are roughly classified into those which have a composition of materials selected to cut off or block ultraviolet rays, and those which have a surface layer capable of cutting off or blocking ultraviolet rays.
The sheets of ultraviolet-cutoff glass of the latter category include a sheet of glass having a multilayer film capable of reflecting or absorbing radiations in an ultraviolet range, and coated on a surface of the sheet by a vacuum deposition process such as evaporation, sputtering, or the like, a CLD such as sol-gel processing, or the like, a sheet of glass having a surface coating agent containing a metal capable of absorbing radiations in an ultraviolet range, and applied or coated in vacuum on a surface of the sheet, and a sheet of glass having a surface coating agent containing an organic material (ultraviolet absorbent: UVA) capable of absorbing radiations in an ultraviolet range and coated on a surface of the sheet.
Certain automobile window glass sheets comprise sheets of heat-reflecting glass coated with a heat-reflecting film for reducing the level of solar energy that enters the passenger's compartment thereby to lessen the burden on the air-conditioning unit combined with the passenger's compartment. One known sheet of heat-reflecting glass has a heat-reflecting film formed on a surface of the sheet of glass, and an over-coat layer (protective layer) formed on the surface of the heat-reflecting film.
If those sheets of ultraviolet-cutoff glass which have a surface layer capable of cutting off or blocking ultraviolet rays are to remain uncolored and also to be as effective to cut off ultraviolet radiations as sheets of laminated glass, then they need to be coated with a surface coating agent that contains an ultraviolet absorbent (UVA). However, if the content of the UVA in the surface coating agent is increased, then the strength and hence surface hardness of the layer of the surface coating agent are lowered, making the layer of the surface coating agent vulnerable to damage. The UVA suffers a complex deterioration in the presence of water upon exposure to ultraviolet rays. For these reasons, the layer of the surface coating agent is required to be coated with a over-coat layer.
The over-coat layer thus coated as a protective layer on the surface coating layer that contains the UVA or the surface of the heat-reflecting film has its own problems. Specifically, it is necessary for the entire manufacturing process to include an additional process of growing the over-coat layer. Since the over-coat layer is normally grown in an oxygen atmosphere, the rate of growth of the over-coat layer is extremely low, resulting in reduced productivity. The sheets of heat-reflecting glass which are combined with the over-coat layer have a glaring appearance because the heat-reflecting film and the over-coat layer have refractive indexes higher than the refractive index of glass.